Method of Manufacturing III Nitride Crystal, III Nitride Crystal Substrate, and Semiconductor Device

ABSTRACT

Affords III-nitride crystals having a major surface whose variance in crystallographic plane orientation with respect to an {hkil} plane chosen exclusive of the { 0001}  form is minimal. A method of manufacturing the III-nitride crystal is one of: conditioning a plurality of crystal plates ( 10 ) in which the deviation in crystallographic plane orientation in any given point on the major face ( 10   m ) of the crystal plates ( 10 ), with respect to an {hkil} plane chosen exclusive of the { 0001}  form, is not greater than 0.5′; arranging the plurality of crystal plates ( 10 ) in a manner such that the plane-orientation deviation, with respect to the {hkil} plane, in any given point on the major-face ( 10   m ) collective surface ( 10   a ) of the plurality of crystal plates ( 10 ) will be not greater than 0.5° , and such that at least a portion of the major face ( 10   m ) of the crystal plates ( 10 ) is exposed; and growing second III-nitride crystal ( 20 ) onto the exposed areas of the major faces ( 10   m ) of the plurality of crystal plates ( 10 ).

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to methods of manufacturing III-nitridecrystals and III-nitride crystal substrates having a major surface whosevariance in crystallographic plane orientation, with respect to an{hkil} plane that is a crystallographic plane chosen exclusive of the{0001} form, is slight (h, k, i and l herein being whole numbers, withthe relationship i=−(h+k) holding—likewise hereinafter). The presentinvention also relates to methods of manufacturing semiconductor devicesincluding such III nitride crystal substrates.

2. Description of the Related Art

Group-III nitride crystals, which are employed advantageously inlight-emitting devices, electronic devices and semiconductor sensors,are ordinarily manufactured by growing crystal onto the major surface ofa sapphire substrate having a (0001)-plane major surface, or onto a GaAssubstrate having a (111) α-plane major surface, by means of avapor-phase technique such as hydride vapor-phase epitaxy (HVPE) ormetalorganic chemical vapor deposition (MOCVD), or by flux growth orother liquid-phase technique. Consequently, ordinarily obtainedIII-nitride crystals have a major surface whose crystallographic planeorientation is {0001}.

With light-emitting devices on substrates that are III-nitride crystalhaving a major surface whose crystallographic plane orientation is{0001}, and in which a multiquantum-well (MQW) structure as alight-emitting layer has been deposited on the major surface, thelight-emission efficiency is compromised by spontaneous polarizationthat occurs within the light-emitting layer owing to the III-nitridecrystal's <0001>oriented polarity. Consequently, the manufacture ofIII-nitride crystal having a major surface whose plane crystallographicorientation is other than {0001} is being sought.

The following several methods have been proposed as ways of creatinggallium-nitride crystal having a surface plane orientation of choice,without influencing the crystallographic plane orientation of the majorsurface of the substrate.

Japanese Unexamined Pat. App. Pub. No. 2005-162526 (Patent Document 1)for example discloses a method in which a number of rectangular crystalboules are sliced from GaN crystal grown by vapor deposition, andmeanwhile, a silicon oxide film is coated onto the surface of aseparately readied sapphire substrate, and then a number of recessesreaching to the substrate are formed in the film, the numerous crystalboules are embedded into the recesses in a manner such that their topsurfaces will have the same desired plane orientation of choice, and byvapor deposition with the crystal boules as seeds, gallium nitridecrystal having a surface plane orientation of choice is grown.

Furthermore, Japanese Unexamined Pat. App. Pub. No. 2006-315947 (PatentDocument 2) discloses a method in which a number of nitridesemiconductor bars are arranged in such a way that the c faces ofadjoining nitride semiconductor bars oppose each other and the m face ofeach nitride semiconductor bar is the upper face, and nitridesemiconductor layers are formed onto the upper face of the thus arrangednitride semiconductor bars.

Patent Document 1: Japanese Unexamined Pat. App. Pub. No. 2005-162526Patent Document 2: Japanese Unexamined Pat. App. Pub. No. 2006-315947

With the method in the just-noted Patent Document 1, however, inasmuchas growth of the GaN crystal is carried out with, as seeds, the boulesof crystal GaN that have been embedded into the sapphire substrate, dueto the disparity in thermal expansion coefficient between sapphire andGaN, fractures and strain occur in the GaN crystal when the crystal iscooled following the growth process, such that GaN crystal of superiorcrystallinity has not been obtainable.

Furthermore, if III-nitride crystal containing Al—for example,Al_(x)Ga_(y)In_(l−x−y)N (x>0, y>0, x+y≦1)—is grown by the method inabove-noted Patent Document 1, because the Al precursor is not selectivewith respect to the silicon oxide film, the Al_(x)Ga_(y)In_(l−x−y)Ngrows onto the silicon oxide film as well, and consequentlyAl_(x)Ga_(y)In_(l−x−y)N crystal of superior crystallinity has not beenobtainable.

With the method in just-noted Patent Document 2, meanwhile, inasmuch asthe c-planes of the nitride semiconductor bars are set in opposition,nitride semiconductor layers having a chosen crystallographic planeorientation other than planes (such as the m-plane, for example)perpendicular to the c-plane have not been obtainable.

Moreover, the nitride semiconductor bars used in the method ofabove-noted Patent Document 2 are rectangular striplike slices of anitride semiconductor wafer grown onto a dissimilar wafer, such assapphire, SiC, silicon or GaAs, having a chemical composition that is ofa different kind from that of the nitride semiconductor. In this case,the nitride semiconductor wafer grown onto the dissimilar waferpossesses significant crystal strain and warp, on account of which thevariance in crystallographic plane orientation, with respect to them-plane, across the major surface of nitride semiconductor bars slicedfrom such a nitride semiconductor wafer is considerable. For thatreason, nitride semiconductor layers grown onto the m-plane of theplurality of nitride semiconductor bars also prove to have considerablevariance in crystallographic plane orientation across the major surfacewith respect to the m-plane. Such inconsistency compromises the deviceproperties of semiconductor devices that incorporate such nitridesemiconductor layers, and is deleterious to production yields.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention, to resolve the problems discussedabove, is to make available a method of manufacturing III-nitridecrystals, III-nitride crystal substrates, and semiconductor devicesincorporating the III nitride crystal substrates, having a major surfacewhose variance in crystallographic plane orientation with respect to an{hkil} plane, being a crystallographic plane chosen exclusive of the{0001} form, is slight.

The present invention, in accordance with one aspect thereof, is aIII-nitride crystal manufacturing method provided with: a step ofslicing a plurality of crystal plates from a first III-nitride crystaland conditioning the plurality of crystal plates to deviation incrystallographic plane orientation in any given point on the major faceof each crystal plate, with respect to an {hkil} plane being acrystallographic plane chosen exclusive of the {0001} form, of notgreater than 0.5′; a step of arranging the plurality of crystal platesin a manner such that the plane-orientation deviation, with respect tothe {hkil} plane, in any given point on the major-face collectivesurface of the plurality of crystal plates will be not greater than0.5°, and such that at least a portion of the major face of each crystalplate is exposed; and a step of growing second III-nitride crystal ontothe exposed areas of the major faces of the plurality of crystal platesin such a way as to incorporate and unify first crystal regions thatgrow onto the exposed areas of the major faces of each crystal plate,and second crystal regions that are regions where the first crystalregions merge with each other.

With a III-nitride crystal manufacturing method involving the presentinvention, in the step of conditioning the plurality of crystal plates,it is possible to have the deviation in crystallographic planeorientation in any given point on the major face of each crystal plate,with respect to an {hkil} plane, be not greater than 0.2° , and in thestep of arranging the plurality of crystal plates, to have theplane-orientation deviation, with respect to the {hkil} plane, in anygiven point on the major-face collective surface of the plurality ofcrystal plates be not greater than 0.2°.

In addition, the present invention, in accordance with another aspectthereof, is a method of manufacturing a III-nitride crystal substratefrom second III-nitride crystal obtained by the manufacturing method setforth above, the III-nitride crystal substrate manufacturing methodbeing provided with a step of forming on the second III-nitride crystalmajor surfaces perpendicular to the growth axis of the secondIII-nitride crystal.

The present invention, in accordance with yet another aspect thereof, isalso a method of manufacturing semiconductor devices incorporating aIII-nitride crystal substrate obtained by the manufacturing method setforth above, the semiconductor device manufacturing method beingprovided with a step of preparing a III-nitride crystal substrate thatincludes the first crystal regions and the second crystal regions; and astep of forming semiconductor devices with the III-nitride crystalsubstrate.

The present invention affords a method of manufacturing III-nitridecrystals, III-nitride crystal substrates, and semiconductor devicesincorporating the III nitride crystal substrates, having a major surfacewhose crystallographic plane-orientation variance with respect to an{hkil} plane, being a crystallographic plane chosen exclusive of the{0001} form, is slight.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A through 1C are outline diagrams illustrating one example of amethod, involving the present invention, of manufacturing III-nitridecrystal and III-nitride crystal substrates. Therein, FIG. 1A is anoblique view summarily representing a step of conditioning a pluralityof crystal plates; FIG. 1B is an oblique view summarily representing astep of arranging the plurality of crystal plates; and FIG. 1C is asectional view summarily representing a step of growing III-nitridecrystal, and a step of forming a major face on the III-nitride crystal.

FIG. 2 is a sectional view summarily representing another example of amethod, involving the present invention, of manufacturing III-nitridecrystal.

FIG. 3 is sectional view summarily representing still another example ofa method, involving the present invention, of manufacturing III-nitridecrystal.

FIG. 4 is a sectional view summarily representing one example ofsemiconductor devices involving the present invention.

In the drawings, reference mark 1 indicates first III-nitride crystal;reference marks 1 m, 10 m, 20 g, 20 m, and 20 n, major (sur)faces;reference mark 10, crystal plates; reference mark 10 a, collectivesurface; reference mark 10 t, edge faces; reference mark 20, secondIII-nitride crystal; reference mark 20 p, III-nitride crystal substrate;reference mark 20 s, first crystal region; reference mark 20 t, secondcrystal region; reference mark 40, semiconductor devices; reference mark41, semiconductor layer; reference mark 42, Schottky contact; referencemark 43, ohmic contact.

DETAILED DESCRIPTION OF THE INVENTION

In crystallography, in order to represent the crystallographic planeorientation of crystal faces, notation (Miller notation) such as (hkl)and (hkil) is used. The crystallographic plane orientation of crystalfaces in crystals of the hexagonal crystal system, such as III-nitridecrystal, is expressed by (hkil). Herein, h, k, i and l are whole numbersreferred to as Miller indices, where the relationship i=−(h+k) holds.The plane of the crystallographic plane orientation (hkil) is called the(hkil) plane. And the direction perpendicular to the (hkil) plane (thedirection of a line normal to the (hkil) plane) is called the [hkil]direction. Meanwhile, “{hkil}” generically signifies crystallographicplane orientations comprehending (hkil) as well as each of itscrystallographically equivalent plane orientations, and “<hkil>”generically signifies directions comprehending [hkil] as well as each ofits crystallographically equivalent directions.

Embodying Mode 1

Reference is made to FIG. 1: One mode of embodying a III-nitride crystalmanufacturing method involving the present invention provides a step(cf. FIG. 1A) of slicing a plurality of crystal plates 10 from a firstIII-nitride crystal 1 and conditioning the plurality of crystal plates10 to a deviation in crystallographic plane orientation in any givenpoint on the major face 10 m of each crystal plate 10, with respect toan {hkil} plane being a crystallographic plane chosen exclusive of the{0001} form, of not greater than 0.5°, and provides a step (cf. FIG. 1B)of arranging the plurality of crystal plates 10 in a manner such thatthe plane-orientation deviation, with respect to the {hkil} plane, inany given point on the major-face 10 m collective surface 10 a of theplurality of crystal plates 10 will be not greater than 0.5° , and suchthat at least a portion of the major face 10 m of each crystal plate 10is exposed, and a step (cf. FIG. 1C) of growing second III-nitridecrystal 20 onto the exposed areas of the major faces 10 m of theplurality of crystal plates 10 in such a way as to incorporate and unifyfirst crystal regions 20 s that grow onto the exposed areas of the majorfaces 10 m of each crystal plate 10, and second crystal regions 20 tthat are regions where the first crystal regions 20 s merge with eachother.

Crystal Plate Conditioning Step

Referring to FIG. 1A, the III-nitride crystal manufacturing method inthe present embodying mode provides a step (crystal conditioning step)of slicing a plurality of crystal plates 10 from a first III-nitridecrystal 1 and conditioning the plurality of crystal plates 10 to adeviation in crystallographic plane orientation in any given point onthe major face 10 m of each crystal plate 10, with respect to an {hkil}plane being a crystallographic plane chosen exclusive of the {0001}form, of not greater than 0.5° .

Conditioning a plurality of crystal plates 10 whose plane-orientationdeviation in any given point on the major face 10 m of each crystalplate 10, with respect to the {hkil} plane, is not greater than 0.5°makes it possible to grow onto the major face 10 m of each crystal plate10 crystal having a major surface of slight plane-orientation deviation.Herein, the plane-orientation deviation in any given point on the majorface 10 m of each crystal plate 10 can be measured by x-raycrystallography in arbitrary points on the major surface of each crystalplate.

Here, from the perspective of further minimizing the deviation incrystallographic plane orientation along the major surface of thecrystal grown, with the plurality of crystal plates 10 it is preferablethat the plane-orientation deviation in any given point on the majorface 10 m of each crystal plate 10, with respect to the {hkil} plane, benot greater than 0.2°.

The step of conditioning the crystal plates, while not beingparticularly limited, is for example carried out in the manner below.The first III-nitride crystal 1 from which the plurality of crystalplates 10 is sliced is not particularly limited, but in generalimplementations are common in which, employing vapor-phase depositionmethods such as hydride vapor-phase epitaxy (HYPE), metalorganicchemical vapor deposition (MOCVD), and sublimation, or liquid-phasedeposition methods such as flux growth, the material is grown using adissimilar substrate—such as a sapphire substrate, an SiC substrate, ora GaAs substrate—whose chemical composition differs from that ofIII-nitride crystal (e.g., materials grown on these dissimilarsubstrates, or materials grown on substrates sliced from III-nitridecrystal grown on such dissimilar substrates), wherein, with the majorsurface ordinarily being the {0001} plane, variance in crystallographicplane orientation across the major surface due to crystal strain isconsiderable.

With reference to FIG. 1A, a plurality of crystal plates 10 is slicedfrom the above-described III-nitride crystal 1. In this operation,slicing so that the major faces 10 m of the plurality of crystal plates10 have an inclination angle θ (0°<θ≦90°) from the major surface 1 m ofthe first III-nitride crystal 1 yields a plurality of crystal plates 10with major faces 10 m having a crystallographic plane orientation nearan {hkil} plane that is a crystallographic plane chosen exclusive of the{0001} form.

Although the angle of inclination θ between the major faces 10 m of thecrystal plates 10 and the major surface lm, being a {0001} plane, of thefirst III-nitride crystal 1 is not particularly limited, from aperspective of reducing the polarity of the major faces 10 m of thecrystal plates 10, the angle preferably is greater than 5°, morepreferably, greater than 40°.

Even with crystal plates 10 obtained in this way, the plane-orientationdeviation, due to crystal strain, along the major face 10 m is large.Consequently, the crystal plates 10 that are sliced off are each scaled(in implementations, as illustrated in FIG. 1, where the crystal platesare square tiles, width W₁×width W₂×thickness T) sufficiently small sothat they may be conditioned to bring the variance in crystallographicplane orientation in any given point on the major face 10 m of eachcrystal plate 10 to no greater than 0.5°. This means that the size ofthe crystal plates will differ depending on the size of the crystalstrain; crystal plates of lower crystal strain can be scaled relativelylarger.

The method of conditioning the sliced-off crystal plates 10 to bring thedeviation in crystallographic plane orientation in any given point onthe major face 10 m of each crystal plate 10 to no greater than 0.5° isnot particularly limited, but from the perspective of ease of theconditioning operation, a method that may be given as a preferableexample is one whereby the crystallographic plane orientation in thecentral portion of a crystal plates' major face is characterized byx-ray crystallography, and the major faces on either side of the crystalplate are ground and/or polished to bring its crystallographic planeorientation, according to objectives, to less than 0.01° with respect tothe chosen {hkil} plane. Herein, it is preferable that the grindingand/or polishing of the major faces on either side of the crystal platesmakes them parallel to each other.

Another preferable, but not particularly limiting, qualification is thatthe edge faces of the crystal plates apart from their major faces be cutperpendicular to the major faces. Forming such edge faces facilitiesarranging the plurality of crystal plates so that the edge faces of eachof the crystal plates contact each other. Here too, the edge faces arepreferably ground and/or polished.

Crystal Plate Arranging Step

Referring now to FIG. 1B, the III-nitride crystal manufacturing methodin the present embodying mode further provides a step of arranging theplurality of crystal plates 10 in a manner such that theplane-orientation deviation, with respect to the {hkil} plane, in anygiven point on the major-face 10 m collective surface 10 a of theplurality of crystal plates 10 will be not greater than 0.5°, and suchthat at least a portion of the major face 10 m of each crystal plate 10is exposed.

Arranging the plurality of crystal plates 10 in the manner justdescribed makes it possible to grow, onto the exposed areas of the majorfaces 10 m of the plurality of crystal plates 10, crystal having a majorsurface in which the variance in crystallographic plane orientation isminimal. Herein, the deviation in crystallographic plane orientation inany given point on the major-face 10 m collective surface 10 a of theplurality of crystal plates 10 can be characterized by x-raycrystallography on randomly selected points on the major-face 10 mcollective surface 10 a of the plurality of crystal plates 10.

In this step as well, from a perspective of further minimizing deviationin the crystallographic plane orientation along the major face of thecrystal that is grown, a plurality of crystal plates 10 whoseplane-orientation deviation with respect to the {hkil} plane in anychosen point on the major face 10 m of each crystal plate 10 is notgreater than 0.2° preferably is arranged so that the plane-orientationvariance with respect to the {hkil} plane in any chosen point over thecollective surface of the plurality of crystal plates is no greater than0.2°.

While the method of arranging the plurality of crystal plates 10 in amanner such that the deviation in crystallographic plane orientation,with respect to the {hkil} plane, in any given point on the major-face10 m collective surface 10 a of the plurality of crystal plates 10 willbe not greater than 0.5° is not particularly limited, one example thatcan be given is a method whereby the plurality of crystal plates 10 isarranged in a manner such that their major faces 10 m parallel eachother.

Furthermore, it is preferable that the plurality of crystal plates 10 bearranged in manner such that the [0001] direction in each crystal plate10 is oriented in the same way. The major faces 10 m of the plurality ofcrystal plates 10 thus arranged each have polarity of the sameorientation as that of the others, therefore making it possible to grow,onto the exposed areas of the major faces 10 m of the plurality ofcrystal plates 10, crystal having a major surface in which the variancein crystallographic plane orientation is even slighter.

Further, the method according to which the plurality of crystal plates10 is arranged so that at least a portion of the major face 10 m of eachcrystal plate 10 is exposed is not particularly limited provided thatunified crystal can be grown onto the major-face exposed areas of theplurality of crystal plates 10, and they can be arranged so that theedge faces 10 t of the plurality of crystal plates 10 are touching, asindicated in FIGS. 1B and 1C, or they can be arranged so that the edgefaces 10 t of the plurality of crystal plates 10 are spaced apart fromeach other, as indicated in FIG. 2, or the plurality of crystal plates10 can be arranged in a manner such that portions of the major faces 10m overlap each other, as indicated in FIG. 3. It will be appreciatedthat in the FIG. 2 instance, in order to grow unified crystal onto themajor-face exposed areas of the plurality of crystal plates 10, theseparation between the edge faces 10 t of the plurality of crystalplates 10 preferably is slight—for example, in implementations where thecrystal that is grown is GaN crystal, preferably 200 μm or less.

Step of Growing Second III-Nitride Crystal

Referring now to FIG. 1C, the III-nitride crystal manufacturing methodin the present embodying mode further provides a step (secondIII-nitride crystal growth step) of growing second III-nitride crystal20 onto the exposed areas of the major faces 10 m of the plurality ofcrystal plates 10 in such a way as to incorporate and unify firstcrystal regions 20 s that grow onto the exposed areas of the major faces10 m of each crystal plate 10, and second crystal regions 20 t that areregions where the first crystal regions 20 s merge with each other.

Growing second III-nitride crystal in the manner just noted producesIII-nitride crystal having an extensive major surface, yet with thevariance in crystallographic plane orientation across that major surfacebeing minimal.

In the step of growing second III-nitride crystal 20, with reference toFIG. 1C and FIGS. 2 and 3, second III-nitride crystal 20 is grown in amanner such that crystal (first crystal regions 20 s) grows onto theexposed areas of the major faces 10 m of the crystal plates 10, and theplural first crystal regions 20 s merge and unify over the edge faces 10t of the a plurality of crystal plates 10. The regions where the firstcrystal regions 20 s merge with each other are here termed “secondcrystal regions 20 t.” Inasmuch as these second crystal regions 20 t arewhere the first crystal regions 20 s merge, the regions' crystallinityis lower, and the dislocation density is higher, than that of the firstcrystal regions 20 s. Consequently, the first crystal regions 20 s andsecond crystal regions 20 t can readily be distinguished by observingunder cathodoluminescence the state of dislocation occurrence.

While the method whereby the second III-nitride crystal is grown is notparticularly limited as long as it is one that allows the crystal to begrown in such a way that the plurality of first crystal regions mergeand unify with one or more of the second crystal regions, examples thatmay be given include vapor-phase deposition methods such as HVPE andMOCVD, and liquid-phase deposition methods such as flux growth.

Since the deviation, from an {hkil} plane, in the crystallographic planeorientation of the major faces 10 m of the plurality of crystal plates10 is not greater than 0.5° (than 0.2°, preferably), the secondIII-nitride crystal grows in approximately an <hkil>direction.

Embodying Mode 2

Reference is made to FIG. 1C: One mode of embodying a III-nitridecrystal substrate manufacturing method involving the present inventionis a method of manufacturing a III-nitride crystal substrate 20 p fromsecond III-nitride crystal 20 obtained according to Embodying Mode 1,and provides a step (major-surface formation step) of forming on thesecond III-nitride crystal 20 major surfaces 20 m, 20 n perpendicular tothe growth axis of the second III-nitride crystal 20. A manufacturingmethod such as this yields III-nitride crystal substrates 20 p havingextensive major surfaces 20 m, 20 n, yet in which variance in thecrystallographic plane orientation along the surfaces 20 m, 20 n isminimal.

In the major-surface formation step of a III-nitride crystal substratemanufacturing method in the present embodying mode, the major surfaces20 m, 20 n are formed on the second III-nitride crystal 20 perpendicularto its crystal growth axis by, specifically, slicing the secondIII-nitride crystal 20 along a plane perpendicular to the<hkil>direction that is its crystal growth axis, or grinding and/orpolishing the major surface 20 g of the as-grown second III-nitridecrystal 20 to form a plane perpendicular to the <hkil>direction. AIII-nitride crystal substrate 20 p having major surfaces 20 m, 20 nperpendicular to the crystal growth axis is thereby obtained.

Meanwhile, slicing the second III-nitride crystal along a predeterminedplane not perpendicular to the <hkil>direction that is the crystal'sgrowth axis, or grinding and/or polishing the major surface of theas-grown second III-nitride crystal to form a predetermined plane notperpendicular to the <hkil>direction yields a III-nitride crystalsubstrate having a predetermined major surface not perpendicular to thegrowth axis of the crystal. The variance in crystallographic planeorientation along the major surface of such a III-nitride crystalsubstrate is minimal.

Embodying Mode 3

Reference is made to FIG. 4: One mode of embodying a semiconductordevice manufacturing method involving the present invention is a methodof manufacturing semiconductor devices incorporating a III-nitridecrystal substrate 20 p obtained according to Embodying Mode 2, andprovides a step (III-nitride crystal substrate preparation step) ofpreparing a III-nitride crystal substrate 20 p incorporating firstcrystal regions 20 s and second crystal regions 20 t, and a step(semiconductor device formation step) of forming semiconductor deviceswith the III-nitride crystal substrate 20 p. A manufacturing method assuch produces semiconductor devices of superior device characteristics,at favorable production yields.

Examples that may be given of such semiconductor devices include, butare not limited to: light-emitting devices such as light-emitting diodesand laser diodes; electronic devices such as rectifiers, bipolartransistors, field-effect transistors, and high electron mobilitytransistors (HEMTs); semiconductor sensors such as temperature sensors,pressure sensors, radiation sensors, and visible-blind ultravioletdetectors; and surface acoustic wave (SAW) devices, vibrators,resonators, oscillators, microelectromechanical system (MEMS) parts, andpiezoelectric actuators.

In the III-nitride crystal substrate preparation step of thesemiconductor device manufacturing method in the present embodying mode,a III-nitride crystal substrate 20 p of Embodying Mode 2 is prepared.The III-nitride crystal substrate 20 p thus incorporates first crystalregions 20 s grown onto the exposed areas of the major faces 10 m of theplurality of crystal plates 10, and second crystal regions 20 t that areregions where the plurality of first crystal regions merge.

And in the semiconductor device formation step of the semiconductordevice manufacturing method in the present embodying mode, the followingsemiconductor devices, for example, are formed. Referring to FIG. 4, asemiconductor layer 41 is formed onto the major surface 20 m of theIII-nitride crystal substrate 20 p on one side, Schottky contacts 42 areformed onto the semiconductor layer 41 at a predetermined pitch, and anohmic contact 43 is formed onto the major surface 20 n of theIII-nitride crystal substrate 20 p on the other side, creatingsemiconductor devices 40. In this case, the Schottky contacts 42 areformed within the regions directly over the first crystal regions 20 s,avoiding the regions directly over the second crystal regions 20 t, ofthe III-nitride crystal substrate 20 p. The semiconductor devices aretherefore formed within the first crystal regions 20 s of theIII-nitride crystal substrate 20 p.

EMBODIMENTS 1. Preparation of First GaN Crystal (First III-NitrideCrystal)

A 2-inch (50.8 mm) diameter GaN undersubstrate with a (0001)-plane majorsurface and a 2-mm radius of curvature (GaN undersubstrate A), and a2-inch (50.8 mm) diameter GaN undersubstrate with a (0001)-plane majorsurface and a 5-mm radius of curvature (GaN undersubstrate B), obtainedby slicing a GaN crystal grown by HVPE onto a 2-inch (50.8 mm) diametersapphire substrate, were prepared.

First GaN crystal (first III-nitride crystal 1), of 12 mm thickness, wasgrown by HVPE onto the respective major surfaces of the thus-preparedGaN undersubstrate A and GaN undersubstrate B (cf. FIG. 1A). Here thefirst GaN crystal grown onto GaN undersubstrate A is termed “GaN crystal1A,” while the first GaN crystal grown onto GaN undersubstrate B istermed “GaN crystal 1B.”

2. Conditioning of Crystal Plates

Referring to FIG. 1A, the GaN crystal 1A (first III-nitride crystal 1)was sliced along a plurality of planes having an inclination angle of62° with respect to the crystal's (0001) major surface lm to manufacturea plurality of 1-mm thick GaN crystal plates A₀ having major facesapproximately on the (1-101) plane. In the same manner, the GaN crystal1B was sliced along a plurality of planes having an inclination angle of62° with respect to the crystal's (0001) major surface to manufacture aplurality of 1-mm thick GaN crystal plates B₀ having major facesapproximately on the (1-101) plane.

The deviation, with respect to the (1-101) plane crystallographic planeorientation, in each of points arrayed at a 1-mm pitch within the (widthW₁: 14 mm×width W₂: 50 mm) major faces of GaN crystal plates A₀ slicedfrom approximately the central portion of the GaN crystal A wasdetermined by x-ray crystallography, whereupon the <11-20>directiondeviation was 1.2° and the <0001>direction deviation was 0.25°.Likewise, the deviation with respect to the (1-101) planecrystallographic plane orientation in each of points arrayed at a 1-mmpitch within the (10 mm×50 mm) major faces of GaN crystal plates B_(o)sliced from approximately the central portion of the GaN crystal B wasdetermined to be a <11-20>direction deviation of 0.47° and a<0001>direction deviation of 0.10°.

Furthermore, the GaN crystal plates A₀ were diced into 11-mm squares toform a plurality of GaN crystal plates C₀. The deviation with respect tothe (1-101) plane crystallographic plane orientation in a central pointin the major faces of the GaN crystal plates C₀ was determined by x-raycrystallography, the major faces on either side of the GaN crystalplates C₀ were ground and polished to bring the deviation to under0.01°, and then the edge faces of the GaN crystal plates C₀ were cutperpendicular to the major face, thereby producing GaN crystal plates C(crystal plates 10) of width W₁: 10 mm×width W₂: 10 mm×thickness T: 0.5mm. In the same way, GaN crystal plates D (crystal plates 10) of widthW₁:10 mm×width W₂: 10 mm×thickness T: 0.5 mm were obtained from the GaNcrystal plates B_(o). Here, the deviation with respect to the (1-101)plane crystallographic plane orientation in each of points arrayed at a1-mm pitch within the major faces of the GaN crystal plates C wasdetermined by x-ray crystallography, whereat the <11-20>directiondeviation was 0.25° and the <0001>direction deviation was 0.24°.Meanwhile, the deviation with respect to the (1-101) planecrystallographic plane orientation in each of points arrayed at a 1-mmpitch within the major faces of the GaN crystal plates D was determinedto be a <11-20>direction deviation of 0.08° and a <0001> directiondeviation of 0.07°.

In addition, the edge faces of the GaN crystal plates A₀ also were cutperpendicular to the major face, whereby GaN crystal plates A (crystalplates 10) of width W₁: 10 mm×width W₂: 50 mm×thickness T: 1.0 mm wereobtained. And in the same way, GaN crystal plates B (crystal plates 10)of width W₁: 10 mm×width W₂: 50 mm×thickness T: 1.0 mm were obtainedfrom the GaN crystal plates B₀. Here, the deviation with respect to the(1-101) plane crystallographic plane orientation in each of pointsarrayed at a 1-mm pitch within the major faces of the GaN crystal platesA was a <11-20>direction deviation of 1.1° and a <0001>directiondeviation of 0.20°. Meanwhile, the deviation with respect to the (1-101)plane crystallographic plane orientation in each of points arrayed at a1-mm pitch within the major faces of the GaN crystal plates B was a<11-20>direction deviation of 0.45° and a <0001>direction deviation of0.07°.

3. Arranging of Crystal Plates

Referring to FIG. 1B, twenty-five GaN crystal plates C (crystal plates10) were arranged five to a side both lengthwise and widthwise, in amanner such that their major faces were parallel and such that theiredge faces were adjoining In this situation, the deviation with respectto the (1-101) plane crystallographic plane orientation in each ofpoints arrayed at a 1-mm pitch within the major-face 10 m collectivesurface 10 a of the twenty-five GaN crystal plates C proves to be a<11-20>direction deviation of 0.25° and a <0001>direction deviation of0.24°. And in the same way, twenty-five GaN crystal plates D werearranged five to a side both lengthwise and widthwise. In thissituation, the deviation with respect to the (1-101) planecrystallographic plane orientation in each of points arrayed at a 1-mmpitch within the major-face 10 m collective surface 10 a of thetwenty-five GaN crystal plates D proves to be a <11-20>directiondeviation of 0.08° and a <0001>direction deviation of 0.07°.

Also, five of the GaN crystal plates A (width W₁: 10 mm×width W₂: 50mm×thickness T: 1 mm) were laid out with the five along the W₁ directionin a manner such that their major faces were parallel and such thattheir edge faces were adjoining In this situation, the deviation withrespect to the (1-101) plane crystallographic plane orientation in eachof points arrayed at a 1-mm pitch within the major-face 10 m collectivesurface 10 a of the five GaN crystal plates A turns out to be a<11-20>direction deviation of 1.1° and a <0001>direction deviation of0.20°. In turn, five of the GaN crystal plates B (width W₁: 10 mm×widthW₂: 50 mm×thickness T: 1 mm) were also laid out. In this situation, thedeviation with respect to the (1-101) plane crystallographic planeorientation in each of points arrayed at a 1-mm pitch within themajor-face 10 m collective surface 10 a of the five GaN crystal plates Bturns out to be a <11-20>direction deviation of 0.45° and a<0001>direction deviation of 0.07°.

4. Growth of Second GaN Crystal (Second III-Nitride Crystal) andManufacture of GaN Crystal Substrate

Referring to FIG. 1C, GaN crystal 2C, being second GaN crystal (secondIII-nitride crystal 20), was grown by HVPE onto the major faces 10 m ofthe twenty-five GaN crystal plates C (crystal plates 10). This GaNcrystal 2C was sliced through planes parallel to the (1-101) plane tomanufacture a 12-mm thick GaN crystal substrate C (III-nitride crystalsubstrate) having major surfaces approximately on the (1-101) plane. Andin the same way, GaN crystal 2D was grown onto the major face 10 m ofthe twenty-five GaN crystal plates D (crystal plates 10), and a 12-mmthick GaN crystal substrate D (III-nitride crystal substrate) havingmajor surfaces approximately on the (1-101) plane was manufactured fromthis GaN crystal 2D.

The deviation with respect to the (1-101) plane crystallographic planeorientation in each of points arrayed at a 1-mm pitch within the majorsurface 20 m of the GaN crystal substrate C (III-nitride crystalsubstrate 20 p) was a <11-20>direction deviation of 0.25° and a<0001>direction deviation of 0.26° . Meanwhile, the deviation withrespect to the (1-101) plane crystallographic plane orientation in eachof points arrayed at a 1-mm pitch within the major surface 20 m of theGaN crystal substrate D was a <11-20>direction deviation of 0.08° and a<0001>direction deviation of 0.08°.

Also, GaN crystal 2A, being second GaN crystal (second III-nitridecrystal 20), likewise as just described was grown by HVPE onto the majorfaces of the five GaN crystal plates A, and this GaN crystal 2A wassliced through planes parallel to the (1-101) plane to manufacture a12-mm thick GaN crystal substrate A (III-nitride crystal substrate)having major surfaces approximately on the (1-101) plane. And in thesame way, GaN crystal 2B, being second GaN crystal (second III-nitridecrystal 20), was grown onto the major faces of the five GaN crystalplates B, and this GaN crystal 2B was sliced through planes parallel tothe (1-101) plane to manufacture a 12-mm thick GaN crystal substrate B(III-nitride crystal substrate) having major surfaces approximately onthe (1-101) plane.

The deviation with respect to the (1-101) plane crystallographic planeorientation in each of points arrayed at a 1-mm pitch within the majorsurface 20 m of the GaN crystal substrate A (III-nitride crystalsubstrate 20 p) was a <11-20>direction deviation of 1.3° and a<0001>direction deviation of 1.5° . Meanwhile, the deviation withrespect to the (1-101) plane crystallographic plane orientation in eachof points arrayed at a 1-mm pitch within the major surface 20 m of theGaN crystal substrate B was a <11-20>direction deviation of 0.5° and a<0001>direction deviation of 0.6°.

Thus conditioning a plurality of crystal plates in which the deviationin crystallographic plane orientation in any given point on the majorfaces of the crystal plates, with respect to an {hkil} plane was notgreater than 0.5° (preferably not greater than)0.2°, arranging theplurality of crystal plates in a manner such that the plane-orientationdeviation, with respect to the {hkil} plane, in any given point on themajor-face collective surface of the plurality of crystal plates was notgreater than 0.5° (preferably not greater than)0.2°, and such that atleast a portion of the major faces of the crystal plates was exposed,and growing second III-nitride crystal onto the exposed areas of themajor faces of the plurality of crystal plates produced III-nitridecrystal and III-nitride crystal substrates having major surfaces ofminimal variance in crystallographic plane orientation with respect tothe {hkil} plane.

Herein, in conditioning the GaN crystal plates (crystal plates 10) inthe present embodiment, adjustment whereby the tilt angle (meaning theangle of deviation from the <hkil>direction, ditto hereinafter) of themajor faces of the crystal plates was reduced was carried out;adjustment whereby the twist angle (meaning the angle of torsionaldeviation in the <hkil>direction, ditto hereinafter) of the major facesof the crystal plates was reduced was not carried out. This is becauseit is the tilt angle that largely influences the properties ofIII-nitride semiconductor layers (III-nitride crystal layers) formedonto the plates. Of course, adjustment to reduce the twist angle shouldbe carried out according to need. For that, the adjustment to reduce thecrystal-plate twist angle should be made when cutting the edge faces ofthe crystal plates.

It should be noted that measuring the electroconductivity (using anEC-80 made by Napukon K.K.) of the obtained GaN crystal substrates A, B,C and D globally across their major surfaces verified a highelectroconductivity of 0.002 S2 cm. This is believed to be becauseoxygen contained in the HVPE growth-ambient gas is taken into the(1-101) crystal-growth plane with a high efficiency.

5. Manufacture of Semiconductor Devices

Referring to FIG. 4, an n-type GaN layer (semiconductor layer 41) of 15μm thickness and 1×10¹⁶ cm⁻³ carrier concentration was formed by MOCVDonto the major surface 20 m of the GaN crystal substrate C (III-nitridecrystal substrate 20 p) on one side. Schottky contacts 42 of 450 μmdiameter, made from Au, were formed by vacuum evaporation depositiononto the n-type GaN layer (semiconductor layer 41) at a 2 mm pitch. Inthis case, the Schottky contacts 42 were formed within the regionsdirectly over the first crystal regions 20 s, avoiding the regionsdirectly over the second crystal regions 20 t, of the GaN crystalsubstrate C (III-nitride crystal substrate 20 p). Further, an ohmiccontact 43 made from Ti/Al was formed onto the major surface 20 n of theGaN crystal substrate C (III-nitride crystal substrate 20 p) on theother side. In this way, semiconductor devices C (semiconductor devices40) were produced. A reverse voltage was applied across the Schottkycontacts 42 and ohmic contact 43 of the semiconductor devices C to testthe withstand voltage performance of the semiconductor devices.

When a withstand voltage of not less than 1000 V was taken to be aconforming product, 295 chips out of 400 chips were conforming products,for a product yield of 74%. Meanwhile, when a withstand voltage of notless than 500 V was taken to be a conforming product, 385 chips out of400 chips were conforming products, for a product yield of 96%.

In the same manner as just described, semiconductor devices D weremanufactured utilizing the GaN crystal substrate D, semiconductordevices A were manufactured utilizing the GaN crystal substrate A, andsemiconductor devices B were manufactured utilizing the GaN crystalsubstrate B.

With regard to the semiconductor devices D, when a withstand voltage ofnot less than 1000 V was taken to be a conforming product, 385 chips outof 400 chips were conforming products, for a product yield of 96%, andwhen a withstand voltage of not less than 500 V was taken to be aconforming product, 395 chips out of 400 chips were conforming products,for a product yield of 99%.

With regard to the semiconductor devices A, when a withstand voltage ofnot less than 1000 V was taken to be a conforming product, 12 chips outof 400 chips were conforming products, for a product yield of 3%, andwhen a withstand voltage of not less than 500 V was taken to be aconforming product, 52 chips out of 400 chips were conforming products,for a product yield of 13%.

With regard to the semiconductor devices B, when a withstand voltage ofnot less than 1000 V was taken to be a conforming product, 84 chips outof 400 chips were conforming products, for a product yield of 21%, andwhen a withstand voltage of not less than 500 V was taken to be aconforming product, 350 chips out of 400 chips were conforming products,for a product yield of 87%.

As set forth above, with larger variance in crystallographic planeorientation along the major surface of a III-nitride crystal substratewithin semiconductor devices, the product yields of the semiconductordevices are severely compromised. This is believed to be because ifvariance in crystallographic plane orientation along the major surfaceof a III-nitride crystal substrate is great, macro-steps occur in thegrowth plane of the semiconductor layers grown onto the substrate'smajor surface, which is detrimental to the morphology of the crystalgrowth plane in terms of its planarity.

As set forth above, when the standard for conforming products is awithstand voltage of not less than 500 V, for III-nitride crystalsubstrates where the major surface is made the (1-101) plane, if thevariance, with respect to the (1-101) plane, in crystallographic planeorientation across the major surface is not greater than 0.5° , thesemiconductor device yields are heightened. Likewise, for III-nitridesubstrates where the major surface is made the (11-22) plane or the(1-100) plane, the variance, with respect to the (11-22) plane or(1-100) plane, in crystallographic plane orientation across the majorsurface should be not greater than 0.5°.

And if the standard for conforming products is a withstand voltage ofnot less than 1000 V, for III-nitride crystal substrates where the majorsurface is made the (1-101) plane, if the variance, with respect to the(1-101) plane, in crystallographic plane orientation across the majorsurface is not greater than 0.2°, the semiconductor device yields areheightened. Likewise, for III-nitride substrates where the major surfaceis made the (11-22) plane or the (1-100) plane, the variance, withrespect to the (11-22) plane or (1-100) plane, in crystallographic planeorientation across the major surface should be not greater than 0.2°.

The presently disclosed embodying modes and embodiment examples shouldin all respects be considered to be illustrative and not limiting. Thescope of the present invention is set forth not by the foregoingdescription but by the scope of the patent claims, and is intended toinclude meanings equivalent to the scope of the patent claims and allmodifications within the scope.

1. A III-nitride crystal substrate comprising: an undersubstrateconstituted by a plurality of first III-nitride crystal plates eachdefining a major face and adjoining one another so as to form amajor-face collective surface, said plates being: conditioned to adeviation in crystallographic plane orientation in any given point onthe major face of each crystal plate, with respect to an {hkil} planebeing a crystallographic plane chosen exclusive of the {0001} form, ofnot greater than 0.5°, and arranged in a manner such that theplane-orientation deviation, with respect to said {hkil} plane, in anygiven point on the major-face collective surface of the plurality ofcrystal plates is not greater than 0.5°, and such that at least aportion of the major face of each crystal plate is exposed; and secondIII-nitride crystal on the major-face collective surface of saidundersubstrate, said second III-nitride crystal incorporating andunifying first crystal regions on the exposed areas of the major facesof each crystal plate, and second crystal regions where the firstcrystal regions merge with each other.
 2. A III-nitride crystalsubstrate as set forth in claim 1, wherein in said plurality of firstIII-nitride crystal plates constituting said undersubstrate: thedeviation in crystallographic plane orientation in any given point onthe major face of each crystal plate, with respect to an {hkil} plane,is not greater than 0.2°; and the plane-orientation deviation, withrespect to the {hkil} plane, in any given point on the major-facecollective surface of said plurality of first III-nitride crystal platesis not greater than 0.2°.
 3. A III-nitride crystal substrate as setforth in claim 1, wherein the second III-nitride crystal has a majorsurface perpendicular to the growth axis of the second III-nitridecrystal.
 4. A III-nitride crystal substrate as set forth in claim 2,wherein the second III-nitride crystal has a major surface perpendicularto the growth axis of the second III-nitride crystal.
 5. A III-nitridecrystal substrate as set forth in claim 3, wherein deviation withrespect to said {hkil} plane being a crystallographic plane chosenexclusive of the {0001} form, in each of points arrayed at a 1-mm pitchwithin the major surface of the second III-nitride crystal is notgreater than 0.6°.
 6. A III-nitride crystal substrate as set forth inclaim 4, wherein deviation with respect to said {hkil} plane being acrystallographic plane chosen exclusive of the {0001} form, in each ofpoints arrayed at a 1-mm pitch within the major surface of the secondIII-nitride crystal is not greater than 0.6°.
 7. A semiconductor devicebuilt on a III-nitride crystal substrate as set forth in claim
 1. 8. Asemiconductor device built on a III-nitride crystal substrate as setforth in claim
 2. 9. A semiconductor device built on a III-nitridecrystal substrate as set forth in claim
 3. 10. A semiconductor devicebuilt on a III-nitride crystal substrate as set forth in claim
 4. 11. Asemiconductor device built on a III-nitride crystal substrate as setforth in claim
 5. 12. A semiconductor device built on a III-nitridecrystal substrate as set forth in claim 6.